In semiconductor devices represented by LSI (large scale integration) using silicon, performance improvement in terms of speed, power consumption, and so on has been achieved by miniaturization. However, in the current situation where a gate length of transistors has reached several ten nanometers, the miniaturization has given rise to adverse effects and does not necessarily lead to the performance improvement. Further, as for the gate length, it is said that about 10 nm is a limit of the physical miniaturization. Under such circumstances, as one technique for improving the performance without depending on the miniaturization, using a material higher than silicon in electric charge mobility as a channel of a transistor has been under consideration.
Examples of such a material are a CNT (Carbon Nano Tube) and a graphene. A graphene is one layer in graphite being a layered crystal and is an ideal two-dimensional material whose carbon (C) atoms are bonded together in a honeycomb shape. A carbon nano tube is a graphene worked into a tubular form. A carbon nano tube and a graphene both have excellent properties, and a graphene has higher affinity to semiconductor processes because of its planar shape. Further, a graphene not only has very high electric charge mobility but also has high thermal conductivity and high mechanical strength.
However, since there is no band gap in a graphene, an on-off ratio cannot be obtained when the graphene is used as a channel as it is. Therefore, several attempts have been proposed to cause a band gap in a graphene. For example, there has been proposed a graphene nanomesh, which has a structure having holes formed cyclically in a graphene. The graphene nanomesh is sometimes called an antidot lattice. Further, as a method of forming a graphene nanomesh, there has been proposed a method which fabricates a nanomesh structure in block copolymer by utilizing a self-assembly phenomenon of the block copolymer and processes a graphene with the nanomesh structure used as a mask.
However, in the graphene nanomesh manufactured by a conventional method, a sufficient band gap cannot be obtained, and even when it is used as a channel, it is difficult to obtain a sufficient on-off ratio.
Non-patent Literature 1: K. S. Novoselov, et al., “Electronic Field Effect in Atomically Thin Carbon Films”, Science, 306, 2004, 666
Non-patent Literature 2: J. Bai et al., “Graphene Nanomesh”, Nature Nanotech 5, 2010, 190
Non-patent Literature 3: D. Kondo et al., “Low-Temperature Synthesis of Graphene and Fabrication of Top-Gated Field Effect Transistors without Using Transfer Process”, Applied Physics Express 3, 2010, 025102
Non-patent Literature 4: X. Liang et al., “Formation of Bandgap and Subbands in Graphene Nanomeshes with Sub-10 nm Ribbon Width Fabricated via Nanoimprint Lithography Graphene Nanomesh”, Nano Lett. 10, 2010, 2454